The invention relates to the detection of signal patterns and, in particular, to the detection of patterns in digital optical signals.
Noise immunity and extremely high bandwidth capacity are only a few of the myriad advantages optical signal transmission enjoys over electronic transmission, particularly within waveguides, such as optical fibers and integrated optics waveguides. Consequently, optical components are rapidly displacing their electronic counterparts in communications and other systems. Yet, in spite of the many advantages accruing to optical operations, many electronic communications components have yet to be replaced by the corresponding optical components. Consequently, optical signals are typically converted to electronic signals, operated upon in some fashion, then converted back to optical signals for transmission. In long distance transmission, for example, dispersion, absorption and other effects degrade an optical signal as it travels along a fiber. Repeaters, spaced at regular intervals are employed to xe2x80x9cclean upxe2x80x9d or regenerate the signals. Typically, the degraded optical signal is converted to an electronic signal. Electronic components are used to regenerate the electronic signal, then the regenerated signal is converted back to the optical realm and sent along the transmission path.
Other components within digital signal transmission systems, such as digital crossconnects and add/drop multiplexers, for example, employ similar optical-electronic-optical signal conversions. Such conversions tend to limit the benefits of optical signal transmission, imposing the switching speed limitations of electronic components on optical signals. Additionally, each signal conversion, from optical to electronic and from electronic to optical, consumes power, exposes the signals to the introduction of errors, and significantly increases the cost of a system.
Many components within a communications system employ components which recognize patterns in serial optical signals. Conventional systems convert the serial optical signal to an electronic signal for pattern recognition, then convert the signal back to the optical regime for further transmission. The reduced costs, higher operating speeds, and reduced power consumption associated with all-optical operation strongly encourage the elimination of such optical-to-electronic-to-optical signal conversions and a component which recognizes optical signal patterns without optical-to-electronic-to-optical signal conversion, would therefore be highly desirable.
An optical pattern detector in accordance with the principles of the present invention includes an optical sensor configured to sense a plurality of optical signals, an optical summer configured to receive and sum the sensed optical signals, and a sampler configured to sample the summed optical signals.
In one aspect of an optical pattern detector in accordance with the principles of the present invention, a serial optical pattern detector employs a plurality of optical couplers arranged in series and separated by optical delay(s) to xe2x80x9ctap offxe2x80x9d a sequential binary optical signal. The optical delay between optical couplers is equal to the xe2x80x9cbit timexe2x80x9d of the sequential binary signal whose patterns are being detected. The tapped optical signals are transmitted to an optical summer, or xe2x80x9coptical multiplexerxe2x80x9d, through equal optical delays and synchronously detected. The detection process may be effected, for example, by a photodetector. The taps may be xe2x80x9cweightedxe2x80x9d to couple different signal levels to different xe2x80x9cbit positionsxe2x80x9d within a detected signal, thereby effecting various forms of optical digital-to-analog conversion.
In another aspect of an optical pattern detector in accordance with the principles of the present invention, a parallel optical pattern detector employs a plurality of optical couplers arranged in parallel to xe2x80x9ctap offxe2x80x9d sequential binary optical signals from a plurality of optical waveguides such as optical fibers, arranged, for example as a high-speed optical xe2x80x9cbus.xe2x80x9d The couplers are situated on the parallel optical waveguides so as to tap synchronized optical signals. For example, with eight optical waveguides transmitting eight serial binary signal bit streams arranged as a parallel byte stream, eight optical couplers would tap the eight waveguides at equal optical delays from the source of the byte-wide optical data stream. As in the case of the serial arrangement, the tapped optical signals are transmitted to an optical summer through equal optical delays and synchronously detected.
The detection process may be effected, for example, by a photodetector. The taps may be xe2x80x9cweightedxe2x80x9d to couple different signal levels to different xe2x80x9cbit positionsxe2x80x9d within a detected signal, thereby effecting various forms of optical digital-to-analog conversion. The optical delays may be fixed or variable, as may the weighting of the tap values between the couplers and summer. The delays, couplers, and summer may be implemented using optical fiber or integrated optics technologies.
The detector may be employed as a framer for SONET, SDH, or other serial binary optical signals, for example. In another aspect of the invention, the pattern detector may be operated as an optical digital to analog converter and, through use of various weightings of the tap values, the detector may directly decode, in the optical regime, voice samples digitally encoded using any of various coding algorithms. Similarly, weightings of the tap values may be set to allow the detector to decode digital video signals in the optical regime.